Production failures of bacterial cultures caused by bacteriophage infection are considered to be one of the major problems in industrial use of bacterial cultures. Bacteriophages have been found for many of the bacterial strains used in the industry, such as species of lactic acid bacteria e.g. Lactococcus sp., Lactobacillus sp., Leuconostoc sp., Pediococcus sp. or Streptococcus sp.
In the food industry lactic acid bacterial starter cultures are widely used for food fermentations. It appears that among members of the lactic acid bacteria Lactococcus sp. are most devastated by bacteriophage infections. A factor, which leads to frequent bacteriophage infections in lactic acid bacterial starter cultures, is the fact that the fermentation conditions in the food industry including the dairy industry are generally non-sterile. Thus, it has not yet been possible to eliminate bacteriophage contamination under these industrial conditions.
The lytic development of bacteriophages involves adsorption of the phages to the host cell surface, injection of phage DNA into the cell, synthesis of phage proteins, replication of phage DNA, assembly of progeny phages and release of progeny from the host. Cell-mediated mechanisms of interference with any of these events can prevent a phage infection. The ability of bacterial cultures to resist bacteriophage infection during industrial use depends to a large extent on host strain characteristics affecting one or more of the above mechanisms.
Lactococcus lactis contains a chromosomal gene (pip) for a membrane protein that serves as a receptor for the prolate bacteriophage c2 and other phages of the c2 species. Currently, an industrial preferred method to make bacteriophage resistant Lactococcus strains is to make a strain where the pip gene is inactivated.
The article (Kraus J. et al, 1998 J. Dairy Science 81:2339-2335) describes construction of a number of commercially relevant Lactococcus lactis strains where the pip gene was inactivated (pip− strains). The pip− strains were completely resistant to prolate bacteriophage of the c2 species but were fully sensitive to small isometric phage sk1 of the 936 species, small isometric phages mm210b and 31 (p335 species) and to the large isometric phage 949 (949 species).
The complete genome of the Lactococcus lactis IL1403 strain has been sequenced and is published in the Genbank database.
yjaE is a gene of the Lactococcus lactis IL1403 strain.
On the filing date of the present invention Genbank Accession no.: AE006322 showed section 84 of the 218 sections of the complete genome of Lactococcus lactis subsp. lactis IL1403. The coding DNA sequence of the yjaE gene was given as CDS sequence from 5892 to 8291. With respect to function was simply said “Hypothetical protein”. It was also said that the yjaE gene has a low homology to the pip gene. More specifically it was said “22% identical to phage infection protein pip.”
Genbank Accession no.: NC—002662 showed the complete sequence of Lactococcus lactis subsp. lactis IL1403. Here the coding DNA sequence of the yjaE gene was given as CDS sequence from 904024 to 906423.
WO01/77334 discloses the complete genome sequence of Lactococcus lactis subsp. lactis IL1403. In this document the yjaE gene corresponds to ORF 900. No function is attributed to this ORF 900. On pages 27-29 are described several genes that are involved in the bacterio-phage resistance. Page 29, lines 2-3 summarizes these bacteriophage related genes as ORF 38, 41, 448, 452, 518, 1461 and 1472.
In summary, from a technical point of view the function of the yjaE gene was unknown at the filing date of the present application.